1. Field of the Invention
The present invention relates generally to a mattress the firmness of which is readily adjustable, and more particularly pertains to an adjustable firmness mattress pillow top construction in which a selectively inflatable cushion is removably incorporated within the pillow top of the mattress.
2. Discussion of the Prior Art
The use of mattresses having inflatable chambers as an integral part of their construction is well known in the art.
For instance, Sevcik U.S. Pat. No. 2,814,053 discloses a mattress construction having structure for inflating the mattress to conform the upper reclining or sleeping surface to a contour desired to give maximum sleeping comfort. The arrangement compensates for any sagging or uneveness developed in the upper surface which might adversely affect the sleeping comfort of the occupant or occupants. The disclosed embodiments generally incorporate an inflatable envelope positioned at the bottom or middle of the mattress, on top of which are placed typical coil springs with a top pad of fibrous material, or alternatively a relatively thick layer of foam material is positioned on top to support a person lying on the mattress. In the disclosed arrangements, the inflatable envelope, which is longitudinally or transversely divisible into multiple sections, permits selective inflation of the sections to compensate for changes in the contour of the mattress caused by wear, etc. The firmness of the mattress is not adjustable, it being determined primarily by the types of coil springs, top pads, or thick layer of foam material.
Smith U.S. Pat. No. 2,823,394 discloses a mattress having a pneumatic core divided into a plurality of independently inflatable cells positioned in an outer flexible envelope. In this arrangement, a top padding is provided on top of the inflatable cells, and although the pneumatic pressures in the cells would undoubtedly have some effect on firmness, the pneumatic cells are provided primarily for support and not as an adjustment for the firmness of the mattress.
Stoughton U.S. Pat. No. 3,421,163 illustrates an orthopedic cushion which serves as a back rest cushion and combines an air cushion with a foam backing. The cushion has a relatively inflexible back board, in front of which is positioned a resilient cushion of a material such as foamed polymer composition. A separate air envelope is positioned in front of the foam cushion, and is adapted to be inflated to provide air cushion support. In this arrangement, the air envelope is provided as an integral part of the support structure, and again is not utilized to adjust firmness.
The prior art does not provide a mattress having a primary support, on top of which an inflatable cushion, covered by a removable mattress pillow top, provides an adjustment for the firmness of the mattress. Moreover, in designing a mattress of this type, it should be borne in mind that a mattress is a complex supporting structure, of elastic and plastic deformability, subject to both static and dynamic stresses. It must be elastic in order to allow a determined amount of depression in response to a load, while not substantially altering the axis of the load, i.e. of the human body lying down. The mattress also has further functions such as that of allowing transpiration of the supported body, and it must also have suitable thermal characteristics. All of these factors must be taken into account in the design of a mattress having an adjustable firmness, making the construction of such a mattress a rather complex project.